This invention relates generally to a device for measuring torsion and, more particularly, to a device for measuring torsional couple on a mechanical element of the type described, for example, in the publication FR-2692986.
This type of device has two magnetic field generators, connected with a first support and situated in the plane of one cross section of a shaft, and two magnetic field detectors, connected with a second support and immobilized in the plane of another cross section of the shaft. The magnetic field detectors deliver a signal which is proportional to the torsional couple on account of the relative angular offset of the magnetic field generators with respect to the magnetic field detectors. Such a device can be mounted directly on any type of mechanical element.
The measuring precision of such a device, in particular in the case of small angular offsets of the detectors with respect to the generators, depends to a great extent on the initial positioning precision of the magnetic field detectors with regard to facing the magnetic transition situated at the junction of two magnets comprising the magnetic field generator. In effect, if the detector is offset with respect to the magnetic transition while no couple is applied to the mechanical element, this generates a nonzero signal whose value varies with the temperature, which disturbs the measurement of the torsional couple.
A known method for remedying this disadvantage is to improve the positioning precision of the detectors by reducing the tolerances concerning the production of the components and the assembly, but this reduction of the tolerances is accompanied by a great increase of the cost of production of the device. Another solution consists of correcting the signal emitted by each detector by means of an electronic circuit suited in such a way as to cancel electronically the base signal emitted by each detector when no torsional couple is applied to the mechanical element. However, this solution leads to the production of a complex device, having a cost that is inappropriate for the simplest applications.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the invention, this is accomplished by providing a device for measuring torsional couple on a mechanical element, comprising two magnetic field generators attached in a first plane of the mechanical element and two magnetic field detectors arranged in a second plane parallel to the first plane and offset with respect to the first plane. The magnetic field detectors are attached on a support having two housings facing the magnetic field generators, each housing receiving a sensor element on which one of the magnetic field detectors is attached. The shape of the housings is suited so as to allow movement of the sensor elements in such a way as to make possible an adjustment of an initial position of a sensitive element of each magnetic field detector on the support.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.